In an electrophotographic image forming method and apparatus, a toner image is transferred from an image carrier to an intermediate transfer medium or a final transfer medium. However, it is difficult to transfer 100% of the toner. Further, in a color image forming method and apparatus adopting a tandem system, there is a problem that an image carrier which transports a toner image of a different color disposed on the downstream side contacts a previously transferred toner image and the previously transferred toner is reversely transferred to the image carrier for the different color disposed on the downstream side. A transfer residual toner is discarded after cleaning, the resultant waste toner should be treated, and therefore, such a transfer residual toner is not desirable from the viewpoint of labor and also an increase in cleaning cost. If the transfer residual toner collected by cleaning is recycled by returning it to a development unit, the powder characteristic of a toner in the development unit becomes broad because the charging characteristic and the attachment force characteristic of the recycled toner are different from those of a new toner, and therefore it is not desirable. Further, in the case of a cleanerless process in which the toner is collected in a development region without cleaning at the time of the subsequent image development operation, the transfer residual toner inhibits exposure or is not collected completely in the development region and is transferred to a transfer medium at the same time in the subsequent image transfer operation, etc. to cause image deterioration, and therefore it is not desirable. In addition to various problems similar to those of the transfer residual toner, in the case of a cleanerless process, a reverse transfer toner has a problem that it is collected in a development unit which develops a toner of a different color, whereby unexpected mixing of colors is caused and it is impossible to stably maintain the color reproducibility of color image, and therefore, it is not desirable.
For solving these problems, an attempt was made to control the attachment force between a toner and an image carrier and/or an intermediate transfer medium. For example, JP-A-2007-01129 proposes that the transfer characteristic is controlled by regulating the amounts of particles having a large particle diameter and a small particle diameter, and particles having a large attachment force and a small attachment force. Similarly, JP-A-2007-004128 proposes that the amount of particles having a high attachment force relative to an average attachment force is controlled. Further, JP-A-2004-037784 proposes that an average attachment force is controlled for improving the transfer characteristic. In these proposals, however, although a distribution of attachment forces as a combination of an electrostatic attachment force and a non-electrostatic attachment force is considered, the attachment force is composed of the sum of an electrostatic attachment force proportional to the square of charge amount of toner and a non-electrostatic attachment force independent of charge amount and the force of an electric field for moving a toner acts only on a charge of the toner. Therefore, even if the attachment force composed of the sum of two forces is the same, if the ratio of the electrostatic attachment force to the non-electrostatic attachment force is different, an electric field necessary for controlling the movement is different, and there arises a problem that it is impossible to strictly control the movement characteristic of the toner under the action of an electric field. JP-A-2000-66441 and JP-A-2000-98656 propose that the non-electrostatic attachment force is suppressed to low relative to the total attachment force. However, there is no teaching therein as to what developer should be used to favorably control the transferability of the developer and reduce the transfer residual amount based on the non-electrostatic attachment force which inevitably exists.